During the initial script for Resident Evil 2 (now called BIOHAZARD 1.5) by Hideki Kamiya, Ada Wong was originally an Umbrella researcher named Linda. During Leon's scenario, she would guide him through the city's sewers to a factory formerly used by Umbrella; here, she would task him to create a vaccine with her to save Marvin Branagh, who had been infected by the mutant William Birkin, before getting killed by one of the creatures contained within the underground laboratory. She also would not have romance with Leon. In her early concept art, her outfit designs mainly consisted of the same red sweater and black pants, along with a small necklace. One concept showed a large green jacket with an Umbrella logo on the back. In the final design, she wore a white Umbrella lab coat, red shirt, khaki shorts, red shoes, and a necklace.
Already in the redefinition of the Noboru Sugimura's script, the name "Ada" was conceived by Kazunori Kadoi to provide a link to John Clemens, the Arklay Laboratory's head researcher mentioned in the original Resident Evil, and her story's scenario was changed. With regard to her design reformulation, due to former series producer Shinji Mikami being a big-time film buff, Ada has several similarities to the protagonist of Nikita (La Femme Nikita); both are skilled female assassins and super spies for mysterious organizations. As femme fatale archetypes, they are equally adept at weaponry, combat, and assassination as they are with using their feminine wiles to catch unsuspecting men off guard. Each have been "reborn" in one way or another, signified by a scene where they look into a mirror and vow to leave their past behind. They share one major flaw: their love for a man (in this case, Marco for Nikita and Leon for Ada), which often conflicts with certain orders they are given. Both women also have a shady black-clad superior whose cool exterior hides a ruthless nature they answer to: Michael for Nikita, and Wesker for Ada. Lastly, Separate Ways' title screen for Resident Evil 4 resembles the poster for Nikita's movie.